In materials processing, a laser processing device is often employed for scanning the areas of the object which are to be processed with a laser beam. The precision in positioning the laser beam usually determines the precision achieved in processing. Exact three-dimensional positioning is required when focusing the laser beam into a processing volume. For high-precision processing, it is usually indispensable, therefore, to hold the object in an exactly defined position relative to the laser processing device. For such applications, the above-mentioned adapter is useful, because it enables fixation of the object to be processed, so that defined ratios can be achieved up to the processing volume. The central region of the adapter thus becomes part of the beam path.
This is necessary, in particular, in micro-processing of materials which have only low linear optical absorption in the spectral range of the processing laser radiation. In such materials, usually non-linear interactions between the laser radiation and the material are utilized generally in the form of an optical breakthrough being generated in the focus of the laser beam. Since the processing effect then only occurs in the laser beam focus, exact three-dimensional positioning of the focal point is indispensable. Thus, exact depth adjustment of the focal position in the beam path is required in addition to two-dimensional deflection of the laser beam. The above-mentioned adapter serves to ensure constant optical conditions and ones that are known with a certain precision in the beam path leading to the object due to the central region of the adapter being part of the beam path and the adapter coupling the object and the laser processing device.
A typical application for such an adapter is the ophthalmic method known as femtosecond LASIK, wherein the laser processing device provided as a therapeutic appliance focuses a laser beam to a focal point on the order of a few micrometers into the cornea. A plasma causing local separation of the corneal tissue is then generated in the focus. By suitable sequential arrangement of the zones of local separation thus generated, macroscopic cuts are realized and a determined partial volume of the cornea is isolated. Then, by removal of said partial volume, a desired change in refraction of the cornea is achieved, thus enabling correction of defective eyesight.
In connection with the LASIK method, a contact lens provided with reference marks is known from U.S. Pat. No. 6,373,571. This contact lens is adjusted by means of a separate measurement device, causing a relatively complex design. An example of an adapter of the aforementioned type is described in EP 1,159,986 A2. While being similar to the contact lens of U.S. Pat. No. 6,373,571, it additionally comprises a periphery in the form of a holder having line marks, which allow visual alignment by the surgeon.
In materials processing by means of laser radiation, there often arises the need to monitor execution of processing. It is desired to be able to observe the processing field during application of the laser radiation. This holds true, in particular, for the aforementioned LASIK method wherein the treating physician has to observe the field of operation. Therefore, the aforementioned laser processing device usually comprises an optical system for imaging the area to which the laser radiation is applied. The image is generated either on a camera or in an intermediate image plane from which direct visual inspection through an eyepiece is then possible. Observation is effected through the central region of the adapter, and it is required for the laser processing device to illuminate the area to which the laser radiation is being applied and which is being observed as the object field.
Since the adapter usually contacts the object to be processed, it is generally required to employ a separate fresh adapter for each object. This is necessary, in particular in ophthalmic methods, under the aspect of sterility. As a consequence, a fresh adapter has to be fixed to the laser processing device, which is then provided as a therapeutic appliance, every time before processing or before surgery. For fixation, it is known from WO 03/002008 A1 to hold the contact glass in a forceps-like means which is locked on the laser processing device. Locking thereof is effected by a collar guided along a rail. The adapter is pushed in transverse to the optical axis in a form-locking manner.
DE 19 831 674 A1 describes the use of a mechanical coupling mechanism wherein a metal rod fixed to a mount of a contact glass at an oblique angle is held in a sleeve by means of a magnet or a solenoid. The sleeve itself is fitted onto a mechanical adjustment mechanism such that the position of the contact glass can be adjusted.
The prior art solutions for the contact glass realizing an adapter all require, on the one hand, a large number of components that are complicated to manufacture and, on the other hand, the fixations used in the prior art lead to units having relatively large structural dimensions. This makes prior art contact glasses disadvantageous for devices which are to be used on a patient without general anesthesia, but only with local anesthesia. The large amount of material required to produce this disposable article is also a disadvantage, in particular under economic and ecological aspects.